What Are Total Dissolved Solids in Drinking Water?

dirty water from above

We all need water to survive, and those of us lucky enough to live in the developed world have many choices when to comes to selecting how we get our drinking water. Some people spend extra money on purified water home delivery services, where the water is delivered in large 5 gallon jugs. Others chose to rely on municipal water supplies and get water straight from the tap, and then use home filtration to mechanically filter out impurities. Either way, we need to make sure the water we drink is from a good source and has been filtered, purified and sanitized for human consumption. So what exactly needs to be filtered out? It depends on the source.

Water coming from the ground well or ground aquifers will have what is referred to as total dissolved solids, or TDS. This refers to dirt, chemicals, bacteria, pathogens and other impurities that are small enough to pass through fine filter membranes and end up in the liquid. This is why it is called dissolved solids. TDS is measured on a part-per-million basis or PPM, and is a standard testing benchmark in water purity measurement. In the United States and Canada, a TDS reading of 500 (500 parts per million, which can also be expressed as 500 milligrams per liter) is the threshold for safe water.

TDS (parts per million)


0 to 300


300 to 600


600 to  900


900 to 1,200


Over 1,200



But dissolved solids can be both organic and inorganic, which creates another layer of detail required to evaluate the quality and safety of drinking water. Groundwater naturally contains higher levels of organic solids including inorganic salts like magnesium, calcium, potassium and sodium, which is generally safe at lower levels. In fact, premium alkaline bottled water, high in pH is generally considered to taste better because of these minerals. Dissolved organic solids, like mineral, can also create ‘hard water’ which can clog up appliances like washing machines, dishwashers, coffee machines and the like. Because hard water from the ground is prevalent in certain parts of the US, water softening services and devices are quite popular. Inorganic matter is a different story. Sulfate, iron, manganese, petroleum, pathogens, and other man-made contaminants create much more danger when to come to drinking water, and contribute to TDS.

Measuring the TDS in drinking water is essential to maintain safe drinking water supplies for the general public. When a water source has a high level of TDS, it is likely that there are some harmful contaminants in the water. TDS is also easy to measure and if something is happening to water, such as pollution, and chances are TDS levels will change, so keeping track of these changes can act as an early warning signal that something wrong is going on with the water. For these reasons, it is important to monitor the TDS levels in public water, so that if they change, action can be taken immediately. If you’re interest in measuring the TDS in your tap water home, you can buy an in inexpensive tool here. For more information about how TDS is measured and how we can all maintain safe water supplies, please visit the Safe Drinking Water Foundation website.

Photo by Ivan Bandura on Unsplash

by Steve Jortsman